Bone Morphogenetic Proteins (BMPs) are multi-functional regulators of development and differentiation. They exert their functions by regulating cell fate, proliferation, differentiation, and survival. Our preliminary results have shown that several murine genes encoding BMPs (Bmp4, Bmp7, and Bmp8a), BMP receptors (Alk3, Alk6, and Talk), and a downstream signal transducer (Smad1) are expressed in the developing and adult epididymides. Furthermore, mutations in Bmp8a and Bmp8b lead to vacuole formation in the epididymal epithelium, granuloma formation, and male infertility. These data support a hypothesis that multiple genes of the BMP signaling pathways have overlapping roles in controlling the development and functions of the epididymis. The goal of this application is to test the hypothesis by a combination of sophisticated genetics approaches and retrovirus-mediated gene transfers. Specific Aim 1 is designed to further investigate the roles of BMP signaling components (Bmp7, Alk3, and Smad1) and the testis-derived BMPs is the functional maintenance of the adult epididymides. In this aim, the functions of Bmp7 will be studied by creating double mutants with Bmp8a and by further examining the severity of the epididymal defects in these double mutants. Furthermore, the regulation of Bmp7 expression during postnatal epidiymis development by testicular factors and androgens will be investigated as part of our long-term goal to dissect the molecular mechanisms controlling the growth and development of the epididymis. A transgenic over-expression of Bmp8a in the male germ cells will be used to further reveal the functions of testis-derived BMPs in the maintenance of the adult epididymus. The roles of Alk3 and Smad1 in mid- to distal epididymides will be investigated by the Cre/lox recombination system. In Specific Aim 2, the roles of BMP signaling components in postnatal epididymis development will be investigated. Bmp7 null mutants and Bmp7/Bmp4 double mutants will be used to address the roles of these genes in the development of early postnatal epididymides. Moreover, a retrovirus vector, RCAS-Cre, will be used to inactivate Alk3 and Smad1 in the development of mid-pubertal epididymides. The results obtained from these investigations will add significantly to our understanding of the molecular mechanisms controlling the epididymis development and functions.